I've found very few Enterprise customers comfortable with NET 30 terms. We're an interactive agency any deal we do is worth a considerable percentage of our annual income so we don't get too hung up on payment terms unless we're in a cash crunch. NET 30 is "nice" but if you can't do a deal because the terms are NET 60 instead of 30 then you need to figure out why cash is so low...

I've had 45/75 and once 90 day terms forced down my throat. That being said a lot of my clients who have really long payment cycles can be very flexible with us on billing milestones (like 50%+ up front - heck we've had 90% "down" in decembers).

These days all my invoices are done electronically and I have to be honest at least for us we don't often get bills more than a day or two late. I have however learned when we were smaller that generally if something was more than 4-5 days late something was off on the invoice being processed. I stopped giving folks leeway more than about 3 days before I started hounding folks. YMMV.